EFFECTS OF ACID AEROSOL EXPOSURE ON THE SURFACE-PROPERTIES OF AIRWAY MUCUS

It was hypothesized that the mucous layer lining the tracheas of rats and guinea pigs contains surfactant material capable of lowering the a ir/mucus surface tension, gamma, and that exposure to an irritant aero sol would raise the gamma. The gamma of the surface film was measured directly by a spreading droplet technique and indirectly by displaceme nt of polymethyl methacrylate particles into the aqueous layer. The mo rphology of the mucous film was examined by electron microscopy after nonaqueous fixation. gamma was 33.3 +/- 0.70 (SE) mN/m and 32.3 +/- 0. 68 (SE) mN/m for tile normal rat and guinea pig trachea, respectively. Exposure for 4 h to aerosols of sulfuric acid (94.1 +/- 18.68 (SD) an d 43.3 +/- 4.57 (SD) mg/m(3)) caused a several-fold increase in thickn ess of the mucous layer with exudation of protein-like material. Tile osmiophilic surfactant film at the air/mucus interface became irregula rly thickened and multilayered. Despite these morphological changes ga mma remained low, 33.2 +/- 0.43 (SE) mN/m and 32.6 +/- 0.60 (SE) mN/m for rats and guinea pigs, respectively, and displacement of particles into the subphase was not compromised. Tile results indicate that rode nt tracheas are able to maintain a low surface tension in the presence of injury.